1. Field of the Invention
The present invention relates to a method for manufacturing a substrate for liquid-ejecting heads and a liquid-ejecting head.
2. Description of the Related Art
For silicon substrates, etching using a basic aqueous solution such as tetramethylammonium hydroxide (TMAH) solution may proceed at different rates depending on the orientation, and this allows for anisotropic etching of silicon substrates. Liquid-ejecting heads, represented by inkjet recording heads, usually have a silicon oxide layer formed on the silicon substrate, and this silicon oxide layer is insusceptible to etching. With this layer as a mask, silicon substrates undergo anisotropic etching to obtain a supply port for ink or some other kind of liquid.
Some patent publications have disclosed methods for manufacturing a liquid-ejecting head in which a liquid supply port is formed by this technique, namely, anisotropic etching.
FIGS. 5A to 5C illustrate an example of such methods, the method disclosed in U.S. Pat. No. 7,323,115. A silicon substrate 101 has energy-generating elements 102 arranged on either surface, and the opposite surface is covered with a silicon oxide layer, which serves as an etching mask 103, and a protection layer 104 for the etching mask 103 as illustrated in FIG. 5A. Then, as illustrated in FIG. 5B, the silicon substrate 101 undergoes anisotropic etching using TMAH solution to obtain a liquid supply port 106. During this step, the silicon substrate 101 is etched not only in the thickness direction but also in the horizontal direction, or in the direction perpendicular to the thickness direction, and thus the edge around the opening of the etching mask 103 is left protruding as a burr 105. This burr 105 may snap during mounting or assembly of the liquid-ejecting head and enter the liquid flowing from the supply port to ejection ports. So, this burr 105 is usually removed by etching using a mixed solution of hydrofluoric acid, ammonium fluoride, and other necessary components as illustrated in FIG. 5C.
Methods like this one, in which a burr left as a part of an etching mask is removed using a mixed solution containing hydrofluoric acid and ammonium fluoride, require making the burr easy to remove by asking of the inside of the supply port or some other surface treatment for improved wettability. And, there has been increasing demand for closer contact between a liquid-ejecting head and a substrate supporting it. This demand would be satisfied by forming a liquid supply port and then removing the silicon oxide layer and its protection layer to expose the back surface of the silicon substrate; however, this step may be burdensome to manufacturers.